A range of despicably isn't necessarily desirable in all stories, but in some genres, the use of this attribute proves advantageous. The more that people die, the more useful that despicability becomes.
Death in a story provides energy and emotion, and that energy is best off going somewhere, of motivating other characters, and most especially of making the reader feel some emotion.
In a horror story, especially one with multiple characters, the writer begins by killing the most despicable character, the one that you already secretly want to die. The one that you dislike the most. The one who you don't care about. As the worst character dies first, a less horrible character must die next, and so on, creating a vector, a direction, pointing a threat at the most liked character. With each death, your anxiety goes up, while the probability of your favorite character declines because the evil proves itself effective over and over again. Those who die don't find a way out. As they try different things, you slowly become convinced that your favorite character has no way out. Death becomes certain. The climax comes with the favored protagonist striving against the evil.
In a revenge story, the vector points in the opposite direction. To get the maximum satisfaction, the evil begins with the least despicable character (and usually the least competent), proving to us that the revenger has the means to act, and demonstrating that the most despicable character is now under threat. As the story progresses, the acts of revenge grow more satisfying. As the targets become more competent, each success eats away at that character's confidence, until we get the satisfaction of seeing that despicable character break, becoming a pathetic character before their death. The climax is when the most despicable is now alone, his fate certain, and his fall the furthest. In the end, he will be the most pathetic.
The death of the least to the worst also works in heroic fantasy. Often enough, the heroes begin by besting the villain's henchmen as they work up to defeat the villain himself. At the end is always the biggest bad. If you were to turn that around, you would get heroes who defeat the big bad, then feel pettier and pettier as they kill their way down his surviving henchmen. By the time that you get to the lowest one, your heroes wouldn't seem very heroic at all.
War stories provide a third way of killing characters: randomly. The bombs don't care where they fall. Bullets don't choose. In such stories, you see characters who ought to live get shot, and those who should die get promoted. There seems to be no rhyme or reason behind this, and that is, quite frankly, disturbing to the reader. The amoralness of war is emphasized in this haphazard treatment of the living and the dead. The climax in such a story often revolves around saving somebody who is worth saving because you've seen too much randomness.
You can vary this as well. In heroic fantasy, you can kill off the best and most noble characters one by one, working your way down to the least and most conflicted hero, using that energy to slowly transform the least into the best. In this way, you can redeem a villainous character.
A side-effect of this is that a variety of despicableness de-flattens your characters. While this variety doesn't add depth per-say, the varieties of despicableness do add the illusion of depth simply be creating contrasts between characters.